The present invention relates to a continuously variable traction roller transmission.
A previously proposed continuously variable traction roller transmission is disclosed, for example, in JP-A 4-29659. This continuously variable traction roller transmission includes a first traction roller transmission unit having a first input disk, a first output disk and a pair of first traction rollers which come in frictional contact with the two first disks, and a second traction roller transmission unit having a second input disk, a second output disk and a pair of second traction rollers which come in frictional contact with the two second disks. The first and second output disks are arranged to be adjacent to each other. The first input disk is supported to an input shaft on the outer periphery through a ball spline. The input shaft is coupled with a forward/reverse change-over mechanism and a torque converter so as to input engine torque through the two. A biasing force generator is arranged to the first input disk on the rear side thereof. The second input disk is coupled with the input shaft through a ball spline. The second input disk undergoes a force toward the second output disk from a dish plate which in turn undergoes a compressive force from a loading nut engaged with the input shaft. The first and second output disks are rotatably supported on the input shaft through needle bearings, respectively. A driving gear is provided to rotate together with the first and second output disks. The driving gear engaged with a follower connected to one end of an intermediate shaft by a spline so as to rotate together, the intermediate shaft being disposed parallel with the input shaft.
According to such a known continuously variable traction roller transmission, however, there arises the following problem: The biasing force generator is arranged adjacent to the first traction roller transmission unit, which generates a force to be directly transmitted to the first input disk, and thus the first input and output disks produce a force for biasing the first traction rollers. On the other hand, in the second traction roller transmission unit, a force generated by the biasing force generator is transmitted to the second input disk through the input shaft. Since the input shaft is subjected to an axial frictional resistance out of a supporting bearing, etc., the second input and output disks have a relatively reduced force for biasing the second traction rollers as compared with the first input and output disks of the first traction roller transmission unit. Thus, the second traction roller transmission unit is more unstable than the first traction roller transmission unit, resulting in the impossibility of obtaining a predetermined torque capacity.
It is, therefore, an object of the present invention to provide a continuously variable traction roller transmission which has an increased transmission capacity of a second traction roller transmission unit, and an improved stability of the transmission capacity of the entirety of the transmission.